This study investigated the effects of using two types of written advance organizers, key sentences and key vocabulary, on the improvement of EFL learners' listening comprehension. 108 second year university students at the higher and lower listening proficiency levels were randomly assigned to one control group and two experimental groups. Prior to the treatment, all the groups were measured on a listening pretest. The pretest score was used as a covariate to adjust for the initial difference in listening proficiency. Prior to the listening, the first experimental group received a list of key sentences (Previewing Sentences, PS) and the second experimental group received a list of vocabulary items (Vocabulary Pre-teaching, VP). The control group did not receive any kind of advance organizer. After treatment classes, all groups were again measured on a posttest to compare their improvement in listening. The results of the statistical analysis (ANCOVA) showed that the students who received advance organizers demonstrated significant improvement on the listening comprehension posttest while the control group did not. Although participants' listening proficiency had a significant effect on listening comprehension performance, there was no interaction effect between the use of advance organizers and the listening proficiency level. The pedagogical implications of the study are also discussed. (Contains 5 tables and 2 figures.)